Riser Card Question - Mother board short

Hi there,

So recently i aquired a ASROCK 970 Extreme 4. for the purpose of running Multiple GPU's for mining bitcoin/altcoin, and im new to mining.


The Board Slot Configuration Starting closest to CPU/NorthBridge and working down:
1X PCI-E Slot
16X PCI-E Slot
PCI Slot
1X PCI-E Slot
4X PCI-E Slot
PCI Slot
2X PCI-ESlot


I had 3 GPU's to hook up,

I had a Powered USB PCI-E 1X to 16X Riser Card Installed on the very first 1X PCI-E Slot

I had a card directly mounted in the 16X PCI-E Slot, this first primary card was blocking the following PCI Slot and the 1X PCI-E Slot

So for the Third GPU, i plugged another, identical PCI-E 1X to 16X Riser Card into the 4X PCI-E Slot for my third and final GPU,

i powered the board and got a post and noticed the 4X PCI-E Slot with the rise card starting to smoke

A Picture of this can be seen here :
http://imgur.com/a/Is4uf

Any way, i pulled the plug and tried to boot and the board still posts but im afraid to use this slot.
The strange thing is, the guy i bought the board from had another identical board, so i bought another one off him... You would think i would have learned a lesson the first time but no... i did the exact same thing on the second board... it still posts... i just feel stupid,

but i would like to know why this is happening, is it because i must use the PCI-E slots in order and i skipped one? because they share a power bus?, i dont belive the riser cards were at fault, as ive tried numerouse ones in many other situations...